ASTM C1866

Full Name

ASTM C1866 – Standard Specification for Ground-Glass Pozzolan for Use in Concrete

Scope

ASTM C1866 establishes physical, chemical, and performance requirements that ground-glass pozzolan (GGP) must meet to be considered compliant. This ensures that the material will contribute positively to the concrete matrix without introducing harmful contaminants or causing deleterious reactions. Key aspects covered by the standard include:

  • Chemical composition:
    • Limits are placed on the sum of silicon dioxide (SiO₂), aluminum oxide (Al₂O₃), and iron oxide (Fe₂O₃), ensuring sufficient reactive components.
    • Maximum allowable levels for sulfur trioxide (SO₃) and loss on ignition (LOI) are specified to control potentially harmful compounds and organic contaminants.
    • Moisture content is also limited.

  • Physical properties:
    • Fineness: this is crucial for pozzolanic reactivity. ASTM C1866 typically specifies requirements based on the amount retained on a 45-µm (No. 325) sieve and may include requirements related to particle size distribution or specific surface area. Greater fineness generally leads to higher reactivity.
    • Strength activity index (SAI): this performance-based test measures the GGP’s contribution to strength development compared to a control concrete mixture. It requires testing mortar cubes containing GGP at specific ages (typically 7 and 28 days) and comparing their compressive strength to control cubes made only with portland cement. The GGP mix must achieve a minimum percentage of the control strength.
    • Water requirement: the standard limits the amount of additional water needed to achieve a certain flow when GGP is used, compared to a control mix. This controls the impact on concrete workability.
    • Soundness (autoclave expansion): this test ensures the GGP will not cause excessive expansion and potential cracking in the hardened concrete due to delayed reactions.
    • Uniformity requirements: limits are placed on the allowable variation in specific gravity and fineness between samples to ensure consistent material supply.

  • Optional requirements:
    • Alkali-silica reaction (ASR) mitigation: one of the significant benefits of GGP can be its ability to mitigate ASR. ASTM C1866 provides optional requirements where the GGP must demonstrate its effectiveness in reducing expansion when tested according to ASTM C1567 (Accelerated Mortar Bar Test) or potentially ASTM C1293 (Concrete Prism Test) under specific conditions. This is a critical performance indicator for regions prone to ASR.

Utilizing ground-glass pozzolan that meets the requirements of ASTM C1866 offers several advantages:

  • Sustainability: diverts waste glass from landfills, conserving resources and reducing the carbon footprint associated with cement production (as GGP replaces a portion of the cement).
  • Enhanced durability: the pozzolanic reaction refines the pore structure of concrete, reducing permeability and increasing resistance to chemical attack (e.g., sulfates, chlorides).
  • Improved long-term strength: while early strength gain might be slower, the ongoing pozzolanic reaction contributes to increased strength over time.
  • ASR mitigation: properly specified GGP can effectively control damaging expansion due to Alkali-Silica Reaction.
  • Quality assurance: adherence to ASTM C1866 ensures that the GGP possesses the necessary characteristics for predictable and reliable performance in concrete.

Resources

Keywords

ground-glass pozzolan; concrete; specification; pozzolan; supplementary cementitious material (SCM); strength activity index (SAI); fineness; alkali-silica reaction (ASR); chemical composition; physical properties; soundness; water requirement; pozzolanic reaction; durability; uniformity

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